Clip machines of the kind referred to are typically used to close bags, pouches, or tubular fill-and-seal packaging (also called casings or gut) filled with a material of liquid to thick pasty consistency, or (in some cases) with granular material. During such an operation, the filling is first introduced into the packaging and in the case of tubular fill-and-seal packaging is subsequently divided into portions by means of displacement elements. Said displacement elements gather and tie the tubular casing in the radial direction and displace the filling in the constriction in the axial direction with respect to the axis of the tube. In the area where the casing is gathered and tied, a braid of casing material is formed. In the next operating cycle, one clip, or in the case of a double clip arrangement two clips are applied to the gathered casing by means of two (or four) closing tools moved against each other. To achieve this, the first closing lever and a second closing lever for the second closing tool are pivoted out of their open position about what is usually a common pivot axis into the closed position. Each pair of closing tools comprises a punch and a die, between which the clip is shaped until the closed position is reached (the reversal point of movement). Once the packaging has been clipped, the closing tools are returned to their initial or open position by pivoting the closing levers from their closed position back into the open position.
Such clip machines mostly have a crank drive or a cam drive for moving the closing levers, wherein a control curve on a cam disk is picked up by means of a cam roller. To transfer this movement to the closing lever, a simple lever or toggle joint mechanism is used, for example, said lever or toggle joint mechanism being flexed in the open position and straightened in the closed position.
The clip machines of the kind initially described typically use clips made of an embossed aluminum wire strand and each integrally interconnected at the ends of the clip legs in such a way that they span a common plane, the clip plane. The clips are fed in this manner to the closing tools. In the prior art, this occurs along a guide track provided on the (lower) closing lever for the first closing tool, said guide track beginning near the pivot axis of the closing lever and leading to the region of the associated closing tool.
When in the prior art such a chain of clips is transported, the frontmost clip is fed to the first (lower) closing tool by an intermittently engaging feeding means. As long as the frontmost clip is still attached to the chain of clips it is followed by, it is stably held by the latter in the lower closing tool, which is typically in the form of a die.
The pivoting movements of the closing levers are performed with a time shift by means of the drive controller—for example in the form of offset curves on a cam disk and/or by means of an electronic timing control. The lower closing lever is first pivoted into its (upper) closed or end-of-stroke position. In said position, the frontmost clip is pressed against the gathered end of the casing and clamped between the latter and the closing tool. With a time shift, i.e. while the lower closing lever is still in this position, the second (upper) closing tool moves onto the lower closing tool by pivoting about the same pivot axis.
Immediately before the clip is closed, the frontmost clip is separated in this manner from the chain of clips following it, at first by means of a shearing device provided on the closing tools. At this moment, the frontmost clip is free and is pressed against the lower closing tool only by the tension of the gathered end of the casing. The clip is then deformed by the upper closing tool coming closer to the lower closing tool, until the closing tools are the clip height apart and the clip is closed around the gathered end of the casing.
When the clip machine is to be used for many different sausage products and casings, different clips adapted for the respective requirements are applied which differ in respect of both strength and size, e.g. in their leg length and/or thickness of material. The closure gap must be adjusted accordingly, because this is the critical size—referred to hereinafter as the clip height - to which the clip is pressed together during closure. In the prior art, this is achieved by changing the neutral position of at least one of the closing tools, and hence the closure gap. The preferable adjusting means is an adjustable coupling point on the counter bearing of the toggle lever for the second closing tool.
If differently sized clips are used and the closed position is adjusted for this purpose, then the angle between the two closing levers, movable relative to each other, changes. As a consequence, and depending on the leg length of the undeformed clip, the upper closing tool does not engage simultaneously with the two legs. This is shown in very simplified form in FIG. 3, in which the fixed angular position of the lower, non-adjustable closing lever in each case is shown by lines 310, 320 and 330. The angular position of the adjustable upper closing lever is represented in each case by lines 312, 322 and 332. By way of illustration, the drawings show in exaggerated form the position of the closing tools at that moment when the second closing tool (punch) first contacts clips of three different sizes.
In FIG. 3A, one can see that, in the case of a large clip 314, the second closing tool first comes into contact with the inner leg of clip 314 closer to the pivot axis. When the clip is being closed, a torque shown by arrow 316 is first exerted on clip 314. This causes instability of the clip, which after all had already been separated from the chain of clips behind it. In the case of the medium-sized clip 324 in the example shown in FIG. 3B, both legs are contacted simultaneously by the second closing tool 323. Forces are therefore exerted evenly on clip 324 during closure, see arrows 326, and the clip is stabilized in its position when pressed against the first closing tool (die). In the case of a small clip 334, as shown in FIG. 3C, force is applied first to the side further from the pivot axis, and the clip is similarly liable to tilt because of the resultant torque, shown by arrow 336.
It is essential to avoid such uncontrolled tilting moments or torques, which act upon the separated clip and for that reason are a source of error, and thus to make the clip closure process more secure.